Link posted on Design Observer. NY Times article about the design process for New York World Trade Center memorial.
In the end, the designers decided that cut-out letters would work best for rubbings and could be effectively back-lit at night. (The typeface they chose, Optima, was designed by Hermann Zapf in 1958.) Raised letters will indicate categories like Flight 11, North Tower or Engine Company 10.
Even an element so minute had a meaningful consequence. “A big part of the whole issue are the rubbings that people will want to take of the names,” Mr. Rogér said. “That was something we never wanted to lose.”